Previously, a mechanism was developed to brake and/or lock a plate which is moved by slide guides on rails. Typically, the plate is manually driven on the rails and frequently expedients were adopted in order to avoid having to use locking means.
In one configuration, the plate was manually shifted by a lead screw and held in position by resilient return springs which pressed the plate against the end of the screw. When the plate was moved on rails by a lead screw, the plate was held in situ merely by fixing the screw position. This mechanism, however, is incapable of maintaining the plate at an accurate and stable position if the plate is in a situation where it may be upset, as can happen when operations are performed on it at its correct position. One of the upsetting operations involves moving a second plate on the first plate in a direction which is generally orthogonal to the first plate; such an arrangement is generally referred to as a compound table. In a compound table, it is difficult to position the second plate accurately because its movement includes components in the direction of movement of the first plate which is caused by the movement of the second plate. Another typical upsetting operation occurs in response to actions which may be performed on a part arranged on the plate; such an action involves fitting components to a part by welding, using positioning heads and welding heads.